1. Field of the Invention
The present invention relates to an optical-electrical hybrid integrated circuit.
2. Description of the Related Art
In recent years, according to an increase in an integration degree of a semiconductor device, a circuit pattern of an LSI element forming the semiconductor device is further refined. According to the refining of the circuit patterns, a decrease in a sectional area of a wiring leads to an increase in a wiring resistance inevitably. Also a decrease in a space between adjacent wirings causes an increase in an electrostatic capacity between the wirings. Therefore, a signal delay time proportional to a product of an electric resistance and an electrostatic capacity of the wirings increases to cause difficulties in increasing speed of a circuit operation.
Conventionally, a method of reducing a signal delay using multiple wiring layers has been used. However, an increase in a total number of wiring layers means an increase in lithography steps. Cost of lithography steps occupies most of production cost in these days. Thus, the multiple wiring layers lead to an increase in product cost. As a decrease in a wiring resistance means an increase in an electric current, power consumption increases in case of fixed power supply voltage. Therefore, it is necessary to devise another means for a reduction in power consumption.
On the other hand, as a technology for fundamentally solving such a problem of wiring, an optical wiring technology for transmitting a signal using light instead of an electric signal attracts attention. In the optical wiring, an optical waveguide is used for propagation of a signal instead of a metal wiring. Speed of the signal propagating through the optical waveguide depends on only a refractive index of the optical waveguide and is usually about ½ to ⅓ of light speed in the vacuum. Therefore, the optical wiring is prospective as, in particular, a technique replacing a wiring in a long distance. However, power consumption per one light-emitting element used in combination with the optical waveguide is incomparably large compared with power consumption per one usual semiconductor element for operation. Therefore, it is difficult to realize a reduction in power consumption.
To cope with this problem, for example, JP-A 2006-91241 (KOKAI) discloses an optical/electrical composite wiring component that can realize power saving by shutting down an electricity-light conversion unit and a light-electricity conversion unit in an optical wiring.
However, in an optical-electrical hybrid integrated circuit, when the optical wiring is built in a semiconductor integrated circuit, the optical wiring is used in an intermediate section for connecting respective stages of the integrated circuit. Therefore, if the supply of electric power to a light-emitting element is stopped without deliberate thought, signal transmission to circuits in post stages is stopped, and it is likely that normal operations of the circuits is not guaranteed.